Powder image transfer system



Aug. 23, 1966 TSUTOMU HONMA ETAL POWDER IMAGE TRANSFER SYSTEM Flled Nov.27, 1963 T f INVENTOR. n 5 omu Euth l H IDO M Tun-C0 5L2Lrl (Lrrm 27/United States Patent 3,267,840 POWDER IMAGE TRANSFER SYSTEM TsutomuHonma, Kawasaki-sin, and Eiichi Hirano and Tsuneo Yoneyama, Tokyo,Japan, assignors to Tokyo Shibaura Electric Co., Ltd., Kawasaki-sin,Japan, a corporation of Japan Filed Nov. 27, 1963, Ser. No. 326,588 .5Claims. (Cl. 101-1) This invention relates to electrostatic printingapparatus for use in electronic computers, phototelegraphic apparatusand the like, and relates more particularly to an I improved system fortransferring powder images formed on a recording medium to a transfermaterial.

In the conventional process in electrophotography, an exposure platecomprising a thin layer of photoconductive material coated on aconductive backing is given in the dark a uniform electrostatic chargeover its pohtoconductive surface by means of corona charging, and thenexposed to the radiation of radialrays, such as X-rays, through anoriginal image to be reproduced so as to form on the photoconductivesurface an electrostatic latent image corresponding to the pattern orsh-adings of said original image to be reproduced. Thereafter, adeveloping powder formed of pigmented, finely divided resinous particlesand having an electric charge of polarity opposite to that of theelectrostatic latent image is applied on to the electrostatic latentimage and electrostatically deposited thereon thereby forming a visiblepowder image. Transfer of the powder image is carried out by placing atransfer material on said powder image to attract the powder imagecarried on the exposure plate to the transfer material, said powderimage being given an electric charge of polarity opposite to that of thepowder image.

According to another process that has been proposed heretofore, intransferring by placing a transfer sheet or sheets on the powder imageformed on the plate, the chargepolarity of such transfer sheet is variedalternately in every step of replacing transfer sheets so that a largernumber of transfers will be effected.

However, since the above mentioned processes have been developed to bepractical or available in electroph-otography, it is difiicult todirectly apply those techniques, for example, to electrostatichigh-speed printing apparatus used in electronic computers because ofthe differences in plates for forming electrostatic latent images, theamount of developing powders and the like factors. Also in the printingapparatus for electronic computers, it is required to produce, ingeneral, a plurality of reproduction prints.

The principal object of this invention is to provide an improved powderimage transfer system to promote the grade of transferred images whilepreventing corona charging in transfer steps.

Another object of this invention is to provide an improved powder imagetransfer system in which a plurality of reproduction prints can beobtained from a powder image developed on the recording medium byemploying a plurality of transfer apparatus in one cycle of transfersteps.

A further object of this invention is to provide an improved powderimage transfer system wherein a plurality of simultaneous imagereproductions can be successively obtained by supplying developingpowder to the recording medium from which said developing powder may begradually decreased and by repeating developing and transfer steps.

For a better understanding of this invention as well as other objectsand advantages thereof, reference is had to the following detaileddescription of the invention to be read in connection with theaccompanying drawing, in which a single figure represents a diagrammaticview of an embodiment of an electrostatic printing apparatus embodyingthe powder image trans-fer system of this invention.

As shown in the figure, the electrostatic printing apparatus comprisesan insulating recording medium, such for example as, resinous sheet 15of an endless belt type, which is constantly driven by rollers 11, 12,13 and 14. Upon said resinous sheet 15 is formed an electrostatic latentimage by a pulsating voltage from a known printing apparatus 16. Thelatent image thus formed is developed by a known develop-ing apparatus17 as by magnetic brushing or the like, and then developing powder isdeposited thereon. Such developing powder is transported together with atransfer sheet supplied by a payoff station 21 to a first transferdevice 18 through which said developing powder and transfer sheet passand where transfer is effected. In the transfer device 18, the pressroller 19 positioned at a side close to the transfer sheet is formed ofconductive material and charged with opposite polarity to powder image,While the press roller 20 located at a side close to the resinous sheetis formed of insulating material, such as hard rubber. Therefore, thepowder image can be made to adhere to the transfer sheet by the chargingvoltage of the conductive roller 19 while the transfer sheet is passedthrough the rollers 19 and 20. It is to be noted that since the roller20 close to the resinous sheet is made of insulating material, coronadischarging from the roller 19 of the transfer sheet side can beprevented with the result that the latent image bearing surface is freefrom contamination, hence the quality of the transferred image will notbe damaged. Since a single transfer process will leave a residualpowder-image on the sheet, a second transfer device 22 is employed whichwill repeat the transferring functions mentioned above. The functionaldetails of this second transfer device 22 is the same as those describedin connection with the first transfer device 18 with the exception thatcharging voltage as well as pressure imposed on the recording medium bythe rollers are higher than those in the first transfer device. As aresult, the powder image is further decreased to such an extent that itwill not be applicable in the next succeeding transfer operation.However, the powder image carries residual charge which has beenpreviously energized at the printing apparatus 16. Therefore, theresidual latent image is further developed by a developing apparatus 23and developing powder is attractively held thereon. A powder image thusdeposited is again transported to a third transfer device 24 wheretransfer is effected. In this case all the functional details andformation of said third transfer device are the same as those of thefirst transfer device. Repetition of the above first and second transferprocesses will successively produce a number of accurate reproductions.

After image transfer, any residual latent image remaining on the sheetmay be discharged by a discharge device 25 for the transfer steps tofollow in the next sequence of operation. The powder image carried onthe transfer sheet is fixed thereon by means of heat fixing of any knownfixing apparatus 26.

According to the experiments conducted by the inventors, 10-odd accuratereproduction prints having excellent image reproducibility could beobtained by charging a negative electrostatic latent image on therecording medium, under the conditions of the transfer speed of 1m./sec., applied voltage of -1000 v. to the press roller at the transfersheet side of the first transfer device, 1200 v. to the press roller atthe transfer sheet side of the second transfer device, the secondtransfer device imposing upon the recording medium a pressure higherthan that imposed by the first transfer device, and similar voltagesapplied to rollers at the transfer sheet side of the consecutivetransfer devices.

dium a pressure higher than that imposed by the first transfer device,and rollers at the transfer sheet side of the consecutive transferdevices were supplied with a similar voltage.

It should be understood that instead of the press rollers of thetransfer devices other press means of different configuration such asflat plate may be used, and that voltage applied to the rollers facingthe transfer sheets and pressure imposed on the recording medium bythese rollers may be varied with respect to each roller. It should alsobe understood that the recording medium'for electrostatic latent imageformation need not be endless, and that as transfer sheet, sheetscommercially available on the market can be suitably used and areeconomical. In case the recording medium is of sheet type, the recordingmedium may be rolled on a suitable spool after discharging and themedium thus rolled may be repeatedly used in the next succeedingsequence of transfer steps by removing and positioning the spool meansto the position from which the next sequence for latent image formationstarts.

As has been described above, in accordance with this invention, anydesired number of reproduction prints can be consecutively obtained byemploying a desired number of printing apparatus and by supplyingdeveloping powder to cover the shortage in the transfer steps whilefurther developing a residual electrical charge of the latent image,

that is, repeatedly effecting developing and transfer steps toaccomplish continuous transfers. Since the pressing means of thetransfer devices of this invention is formed of conductive material atits side close to the transfer sheet and formed of insulating materialat its side close to the recording medium, corona discharge issubstantially prevented, with the result that transfers with excellentimage reproducibility are achieved. Thus this invention is applicable,for instance, to an electrostatic high-speed printing apparatus inelectronic computer output circuits.

While the present invention has been described in a preferredembodiment, it will be obvious to those skilled in the art that variousmodifications can be made therein within the scope of the invention. Itis intended that the appended claims cover all such modifications.

What is claimed is:

1. A powder image transfer system comprising, means ,for moving arecording medium along a path of travel,

printing means for forming electrostatic latent images on said recordingmedium, a developing apparatus in said travel path for developing thelatent image formed on said recording medium to form visible powderimages, a transfer material payoff station for supplying transfermaterial ed to press said transfer material and recording mediurntogether, said press means having two sections, one section being formedof conductive material positioned closest to the transfer material andanother section formed of insulating material disposed closest to therecording medium, said sections serving to press said transfer materialtherebetween, and means for applying an electric charge to saidconductive material.

2. The powder image transfer system as claimed in claim 1 wherein saidrecording medium is an endless belt and said press means of eachtransfer device is made of cylindrical rollers.

3. A powder image transfer system comprising, means for moving arecording medium along a path of travel, printing means for formingelectrostatic latent images on said recording medium along said travelpath, a developing apparatus for developing the latent image formed onsaid recording medium along said travel path to form visible powderimages, a plurality of transfer devices spaced from each other along thetravel path of the recording medium, each being adapted to effect powderimage transfer on separate transfer material sheets, each transferdevice including press means through which said sheets and recordingmedium pass, for applying pressure to said sheets and recording mediumtherebetween, material on one section thereof disposed for pressing onthe sheet and formed of insulating material on another section disposedfor pressing on the recording medium, and means for applying electriccharges and pressure depending upon the transfer speed to the onesection of each transfer device in such a manner that the electriccharge progressively increases along the path of travel.

4. A device as claimed in claim 3 said pressure applied by said pressmeans increasing progressively along said travel path.

5. A device as claimed in claim 3, wherein said transfer devicesconstitute first, second, and successive transfer stages, there beingadditional developing apparatus along said path of travel past saidsecond stage to further develop the residual latent image on therecording medium.

References Cited by the Examiner UNITED STATES PATENTS 2,756,676 7/ 1956Steinhilper 101-426 2,807,233 9/1957 Fitch 118--637 2,812,709 11/ 1957Gundlach 101426 2,857,290 10/ 1958 Bolton. 2,884,704 5/ 1959 Bolton.2,944,147 7/1960 Bolton.

WILLIAM B, PENN, Primary Examiner.

1. A POWDER IMAGE TRANSFER SYSTEM COMPRISING, MEANS FOR MOVING ARECORDING MEDIUM ALONG A PATH OF TRAVEL, PRINTING MEANS FOR FORMINGELECTROSTATIC LATENT IMAGES ON SAID RECORDING MEDIUM, A DEVELOPINGAPPARATUS IN SAID TRAVEL PATH FOR DEVELOPING THE LATENT IMAGE FORMED ONSAID RECORDING MEDIUM TO FORM VISIBLE POWDER IMAGES, A TRANSFER MATERIALPAYOFF STATION FOR SUPPLYING TRANSFER MATERIAL FOR RECEIVING SAID POWDERIMAGES ON THE RECORDING MEDIUM, A PLURALITY OF TRANSFER DEVICESINCLUDING PRESS MEANS SEQUENTIALLY DISPOSED ALONG SAID TRAVEL PATHADAPT-